1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer and a facsimile machine. More particularly, the invention relates to an image forming apparatus of the type which uses a belt transfer member when an image is transferred onto a recording medium, and improvement of a belt module for use with the image forming apparatus.
2. Description of the Related Art
An intermediate transfer type image forming apparatus maybe exemplified for this type of the image forming apparatus. In the image forming apparatus, a toner image is formed by an image forming unit based on the electrophotography, is primarily transferred onto the intermediate transfer member, and the toner image is secondarily transferred from the intermediate transfer member onto a recording medium.
In this type of the image forming apparatus, to form a color image, color component toner images are primarily transferred onto the intermediate transfer member in successive manner to superimpose those component color toner images. In the primary image transferring process, the images are transferred onto the intermediate transfer member in good conditions. As a result, a good color image suffering from less color misregistration is obtained.
An endless intermediate transfer belt or a cylindrical intermediate transfer drum is generally used for the intermediate transfer member. In most cases, the intermediate transfer belt is used since the respective devices within the image forming apparatus may be laid out at high freedom.
The following proposals are present for the purpose of improving a color image quality. A first proposal is that developing devices containing six color component toners are mounted on a rotary developing unit, thereby improving the color reproducibility of a reproduced image (e.g., JP-A-Hei.10-301402). A second proposal is that with an intention of reproducing a glossy image, a plurality of image forming units using basic four colors, cyan, yellow, magenta, and black, are disposed around the intermediate transfer belt, and an image forming unit using a transparent, clear toner is additionally provided therearound (e.g., JP-A-2000-347476).
In the conventional intermediate transfer type image forming apparatus, the rotary developing unit is size increased by an amount corresponding to the increased number of developing devices. Further, the number of image forming units disposed around the intermediate transfer belt is increased, so that the image forming apparatus is size increased as a whole.
Those technical problems arises not only in the image forming apparatus having the intermediate transfer belt but also in the image forming apparatus having an image bearing belt for supporting images thereon and transporting them.
Accordingly, an object of the present invention is to provide an image forming apparatus which makes more improvement of the color reproducibility of a reproduced image while effectively suppressing the size increase of the whole image forming apparatus, and a belt module for use with the image forming apparatus.
In the image forming apparatus having a belt transfer member such as an intermediate transfer belt, the belt transfer member is generally constructed such that an endless belt is wound on tension rolls. Accordingly, an area occupied by the belt transfer member is determined by the positions of the tension rolls. Therefore, it is possible to secure a space in which the image forming unit is installed by narrowing the space occupied by the belt transfer member. The inventors of the present invention directed their attention to this point, and reached the technical idea of the present invention.
In the following description, reference numerals are added to constituent elements to facilitate understanding the invention. However, the reference numerals do not limit the invention to the following description.
As shown in FIG. 1, according to the invention, there is provided an image forming apparatus having at least one image forming unit 1 (for example 1a to 1d), a belt transferring member 2, a plurality of tension rolls 3 (for example 3a to 3c), and a bending member 5, in which the image forming unit 1 forms a visual image on the belt transferring member 2 to transfer the visual image onto a recording medium 8 through the belt transferring member 2, the belt transferring member 2 has an endless belt 4 wound on the tension rolls 3, the bending member 5 is disposed in outside of the endless belt 4 between at least a pair of tension rolls 3 (for example 3b and 3c) to bend the endless belt 4 toward inside of a tangential line m connected between an outer peripheral ends of at least the pair of adjacent tension rolls 3, the tangential line m and the endless belt 4 define an outer bending concave region 6, and it is possible to dispose an additional image forming unit 7 in the outer bending concave region 6.
In the technique thus constructed, the image forming units 1 may be not only of the electrophotography type and electrostatic recording type, but also of the ink jet type, the magnetrophy type, the elcography type, the offset printing, the gravure printing, and the thermal-transfer printing.
The wording xe2x80x9cat least one image forming units 1xe2x80x9d is used to imply that the image forming apparatus involves a plural-cycle machine with one image forming unit 1 as well as a tandem machine with a plurality of image forming units 1.
If the image forming unit 1 is based on the electrophotography process, the belt transfer member 2 means mainly the intermediate transfer member. If the image forming unit is of the ink jet type, the belt transfer member 2 involves a visual image transport/transfer member which carries the image thereon and transports the image, and transfers the image on a recording medium.
The bending member 5 may appropriately be selected so long as the bending member 5 bends the endless belt 4 toward the inside of a tangential line xe2x80x9cmxe2x80x9d connecting points on the outer circumferences of a couple of tension rolls 3 (e.g., 3b, 3c), and locates the bent endless belt 4 inside the tangential line, is additionally provided outside the endless belt 4 located between at least the couple of adjacent tension rolls 3 (e.g., 3b, 3c). In this case, care must be taken so as not to impair the transportation of the belt transfer member 2, and a disturbance of the visual image.
The endless belt 4 is bent by the bending member 5 and the tension rolls 3 (e.g., 3b, 3c) adjacent to the bending member. The outside bending concave region 6 is secured between the bent part of the endless belt 4 and the tangential line xe2x80x9cmxe2x80x9d.
The outside bending concave region 6 is not specifically limited so far as to allow the image forming unit 7 to additionally be installed therein. In this case, it is not essential whether or not the image forming unit 7 is additionally installed.
To improve the color reproducibility of the reproduced image, the image forming unit 7 is additionally provided within the outside bending concave region 6.
By so doing, even if the image forming unit 7 is additionally provided within the outside bending concave region 6 of the endless belt 4, there is no increase of the apparatus size.
Here, it is essential that the image forming unit 7 is merely installed at the outside bending concave region 6, and it is not essential that it is located completely within the outside bending concave region 6.
In the image forming apparatus of the invention, it is not always needed that the image forming unit 7 is additionally installed. If such a space as to allow the additional installation of the image forming unit is provided, the image forming unit may be additionally installed as an option as desired.
Wit regard to the layout of the bending member 5, the bending member 5 is in contact with the surface of the belt transfer member 2. Therefore, to prevent a disturbance of a visible image on the belt transfer member 2, it is preferable to locate the bending member 5 at a location where the visible image on the belt transfer member 2 is not nipped. To increase a layout freedom of the bending member, it is preferable to locate the bending member 5 at a location where the visible image carried on the belt transfer member 2 is nipped and to design to prevent the disturbance of the visible image.
A preferable specific form of the bending member 5 is a rotary body in order to minimize a contact resistance between the bending member 5 and the belt transfer member 2.
To effectively avoid such a situation that the charged particles forming a visible image or a residual visible image on the belt transfer member 2, attach to the bending member 5, it is preferable that a transfer blocking bias voltage for preventing the transferring mainly of the visual image or the residual visual image on the belt transfer member 2, is applied to the bending member 5.
The transfer blocking bias voltage varies depending on the layout of the bending member 5. Where the bending member 5 is located at a position where the visual image on the belt transfer member 2 passes, a bias voltage the polarity of which is the same as of the charged particles forming the visible image is applied to the bending member, thereby preventing he charged particles from attaching to the bending member 5. Where the bending member 5 is located at a position where the residual visible image on the belt transfer member 2 passes, a bias voltage the polarity of which is the same as of the charged particles forming the residual visible image is applied to the bending member, thereby preventing the charged particles from attaching to the bending member 5.
In this type of transfer blocking bias voltage, to make the transfer blocking effect more reliable, it is preferable to apply an AC bias voltage to the transfer blocking bias voltage at a predetermined duty ratio.
To effectively avoid such a situation that the charged particles forming a visible image or a residual visible image on the belt transfer member 2 attach to the bending member 5, it is preferable that the bending member 5 is electrically earthed, thereby suppressing the charge accumulation on the bending member 5.
In case that the surface property is used for the approach to prevent the visible image or the like from attaching to the bending member 5, the bending member may have a surface protective layer for preventing transferring mainly of at least one of the visual image and a residual visual image on the belt transfer member 2 to the bending member 5.
To make an easy control of the surface potential of the bending member 5, the bending member is preferably a photoreceptor including a surface having a photoconductive and photosensitive layer.
In the embodiment, another device may be used for the charging; however, it is preferable to use natural charging by friction charging for the charging.
Taking easy maintenance into account, it is preferable that the bending member 5 is detachable from the belt transfer member 2.
Further, in the invention, the bending member 5 may be used serving as another functional member. In a preferred embodiment, the bending member 5 serves as a steering member for controlling a meandering motion of the belt transfer member 2.
All those image forming units 1, 7 including the additional image forming unit 7 may be based on the same image forming process (e.g., electrophotography process). Of the image forming processes employed, at least one image forming process (e.g., the combination of the electrophotography process and the ink jet image forming process) may be different from the remaining image forming processes.
For the image forming method for forming a gloss image as the image forming units 1 and 7, it suffices that at least one of the image forming units 1 and 7 forms a gloss transparent layer.
In this case, the gloss transparent layer enhances the surface smoothness, increases the amount of reflecting light, and reduces the amount of scattering light.
In a case where the non-gloss transparent layer is additionally used, it is satisfactory that at least one of the image forming units 1 and 7 forms a non-gloss transparent layer (using transparent particles of 15 xcexcm or larger in particle diameter, and its surface is made coarse or the transparent particles are put therebetween, so that the surface is made coarse.).
For another image forming method for forming the gloss image, at least one of the image forming units 1 and 7 selects one of a glossy colorant and a non-glossy colorant in relation to at least one color component.
In another image forming method by using the image forming units 1 and 7, at least one of the additional image forming unit and the image forming units forms a transparent layer to laminate the transparent layer corresponding to a surface of the recording medium and the remaining image forming units use ink colorant to be impregnated into the transparent layer.
This embodiment is preferable in that a thickness of the colorant is reduced and the fixing property is improved.
An additional image forming method by using the image forming units 1 and 7, is not only an Amplitude Modulation method in which the color component images are layered one on another, but also an Frequency Modulation method in which the color component images are arrayed side by side. If required, both the Amplitude Modulation and the Frequency Modulation may be employed for one image formation.
In a typical embodiment based on the Frequency Modulation, the plurality of image forming units 1 or 7 have color component colorants for forming color images and wherein the image forming units arrange the color component colorants in non-superimposing fashion.
A unit pixel of the color component image by each color component colorant is preferably set to be as small as possible, e.g., 20 xcexcm or less.
Where such an Frequency Modulation is employed, there is no need of using the screen, and hence, generation of moire is prevented. Further, colorant is less wasted.
The invention is not limited the image forming apparatus. Taking account of the possibility that the belt module in which the belt transfer member 2 is bent and disposed is separately marketed, according to the invention, there is also provided a belt module having at least one image forming unit for forming a visual image on the belt transferring member, a belt transferring member, a plurality of tension rolls, and a bending member, in which the belt transferring member has an endless belt wound on the tension rolls, the bending member is disposed in outside of the endless belt between at least a pair of tension rolls to bend the endless belt toward inside of a tangential line connected between an outer peripheral ends of at least the pair of adjacent tension rolls, the tangential line and the endless belt define an outer bending concave region, and the image forming unit is disposed in the outer bending concave region. That is, the present invention is also applicable to a belt module which is provided with the above-mentioned belt transfer member 2 (the outside bending concave region 6 defined by the bending member 5), in addition to the image forming apparatus.
According to the invention, there is also provided an image forming apparatus having an image forming unit for forming a full color image and a transfer member for successively transferring the image formed by the image forming unit, in which a glossy image forming unit is disposed on a side where the glossy image forming unit is opposed to the image forming unit through the image forming unit.
According to the invention, there is also provided an image forming apparatus having an image forming unit for forming a full color image and a transfer member for successively transferring the image by the image forming unit, in which a glossy image forming unit is disposed in a downstream of the image forming unit.
According to the invention, there is also provided the image forming apparatus as above described in which the image forming unit for forming the full color image is capable of forming color images of Y, M and C colors.
According to the invention, there is also provided the image forming apparatus as above described, wherein the additional image forming unit and the image forming units include an ink jet image forming unit.